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Revert "cdc-acm: implement put_char() and flush_chars()" 

This reverts commit a81cf9799a.

The patch causes a regression, which I cannot find the reason for.
So let's revert for now, as a revert hurts only performance.

Original report:
I was trying to resolve the problem with Oliver but we don't get any conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.

I am using simple request-response protocol to obtain the boiller parameters
in constant intervals.

A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
   unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01, 0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.

Before the bad commit everything was working correctly: I've got a requests and
a responses in a timely manner.

After the bad commit more time I am using the kernel module, more problems I have.
The graph [2] is showing the problem.

As you can see after module load all seems fine but after about 30 minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the data.

When I rmmod and insmod the cdc_acm module again, then the situation is starting
over again: running ok shortly after load, and more time it is running, more EAGAINs
I have when calling read().

As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating transmission?)
and I have problems doing read() calls (EAGAIN).

Reported-by: Mariusz Bialonczyk <manio@skyboo.net>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: a81cf9799a ("cdc-acm: implement put_char() and flush_chars()")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oliver Neukum 2018-09-05 17:56:46 +02:00 committed by Greg Kroah-Hartman
parent fa82796609
commit df3aa13c7b
2 changed files with 0 additions and 74 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
drivers/usb/class/cdc-acm.c
View File

@ -780,20 +780,9 @@ static int acm_tty_write(struct tty_struct *tty,
}
if (acm->susp_count) {
if (acm->putbuffer) {
/* now to preserve order */
usb_anchor_urb(acm->putbuffer->urb, &acm->delayed);
acm->putbuffer = NULL;
}
usb_anchor_urb(wb->urb, &acm->delayed);
spin_unlock_irqrestore(&acm->write_lock, flags);
return count;
} else {
if (acm->putbuffer) {
/* at this point there is no good way to handle errors */
acm_start_wb(acm, acm->putbuffer);
acm->putbuffer = NULL;
}
}
stat = acm_start_wb(acm, wb);
@ -804,66 +793,6 @@ static int acm_tty_write(struct tty_struct *tty,
return count;
}
static void acm_tty_flush_chars(struct tty_struct *tty)
{
struct acm *acm = tty->driver_data;
struct acm_wb *cur;
int err;
unsigned long flags;
spin_lock_irqsave(&acm->write_lock, flags);
cur = acm->putbuffer;
if (!cur) /* nothing to do */
goto out;
acm->putbuffer = NULL;
err = usb_autopm_get_interface_async(acm->control);
if (err < 0) {
cur->use = 0;
acm->putbuffer = cur;
goto out;
}
if (acm->susp_count)
usb_anchor_urb(cur->urb, &acm->delayed);
else
acm_start_wb(acm, cur);
out:
spin_unlock_irqrestore(&acm->write_lock, flags);
return;
}
static int acm_tty_put_char(struct tty_struct *tty, unsigned char ch)
{
struct acm *acm = tty->driver_data;
struct acm_wb *cur;
int wbn;
unsigned long flags;
overflow:
cur = acm->putbuffer;
if (!cur) {
spin_lock_irqsave(&acm->write_lock, flags);
wbn = acm_wb_alloc(acm);
if (wbn >= 0) {
cur = &acm->wb[wbn];
acm->putbuffer = cur;
}
spin_unlock_irqrestore(&acm->write_lock, flags);
if (!cur)
return 0;
}
if (cur->len == acm->writesize) {
acm_tty_flush_chars(tty);
goto overflow;
}
cur->buf[cur->len++] = ch;
return 1;
}
static int acm_tty_write_room(struct tty_struct *tty)
{
struct acm *acm = tty->driver_data;
@ -1987,8 +1916,6 @@ static const struct tty_operations acm_ops = {
.cleanup = acm_tty_cleanup,
.hangup = acm_tty_hangup,
.write = acm_tty_write,
.put_char = acm_tty_put_char,
.flush_chars = acm_tty_flush_chars,
.write_room = acm_tty_write_room,
.ioctl = acm_tty_ioctl,
.throttle = acm_tty_throttle,

1
drivers/usb/class/cdc-acm.h
View File

@ -96,7 +96,6 @@ struct acm {
unsigned long read_urbs_free;
struct urb *read_urbs[ACM_NR];
struct acm_rb read_buffers[ACM_NR];
struct acm_wb *putbuffer; /* for acm_tty_put_char() */
int rx_buflimit;
spinlock_t read_lock;
u8 *notification_buffer; /* to reassemble fragmented notifications */